In workplaces where manufacturing processes such as welding are carried out, there may be significant quantities of fumes, gases, vapors, dusts or the like (all of which are generically referred to herein as “fumes”) being produced at various locations. For instance, a work tool such as a welding gun working against a workpiece can produce fumes which need be extracted from the work area.
It is generally desirable that fumes be extracted from a point that is as close as possible from their source. This way, the proportion of fumes being captured can be maximized while the overall air quantity removed from the work area is minimized. In some manufacturing processes, the position of the fume source can change during the operation of the work tool. One example is the arc of an electric welding gun that often moves relative to the workpiece as the weld is being formed. In the case of relatively long welds, the fume hood of a fume extraction system, through which air and fumes are aspirated, may need to be repositioned to remain effective until the welds are completed.
Some fume extraction systems are provided with fume hoods that can automatically follow a fume source have been proposed over the years in an effort to fulfill that need. For instance, the arrangement disclosed in WO 00/25948, published on 11 May 2000, includes an automatic motorized arm for aspirating welding fumes and light sensors for detecting the electric welding arc. A single light sensor with a variable sensitivity is used for the up and down motion of the aspirating hood. This arrangement, however, can only work at a single arc intensity. In practice, the arc intensity not only varies while working on a same workpiece, it also varies greatly from one type of welding process to another. A second limitation of the disclosed arrangement is that it can often cause undesirable erratic motions of the aspirating hood, especially when the arc is initially off centered with reference to the aspirating hood. Hence, the arrangement was not found to be satisfactory.
Accordingly, room for improvements still exists in this area.